1. Field of the Invention
The present invention relates to prosthetic devices particularly shoulder prostheses and, more particularly, to a method and apparatus for replication of angular position of a humeral head of a shoulder prosthesis.
2. Background Information
The state of the prosthetic shoulder market has progressed such that a surgeon generally approaches shoulder replacement surgery in one of two strategic ways. One strategic manner is to perform the shoulder replacement surgery in accordance with a manufacturer""s shoulder prosthesis or shoulder prosthesis product line. Particularly, a surgeon is provided with instrumentation and technique guidelines for the particular shoulder prosthesis or prosthesis line. The guidelines and/or instrumentation direct or dictate the angle of humeral head resection for the implant (prosthesis). This angle is in relation to the humeral intramedullary (IM) canal and is designed to match an optimum set of angles already present in the prosthetic design.
Another strategic manner is to perform the shoulder replacement surgery in accordance with a patient""s anatomy. Particularly, the humeral head is resected according to angles perceived to be xe2x80x9canatomicxe2x80x9d in the opinion of the surgeon, not according to angles already present in the prosthetic design. The prosthesis is designed such that the configuration of the prosthesis is intraoperatively adjustable. This allows the prosthesis to be adjustable whereby it can match the boney preparation.
Even with respect to these two divergent manners of surgical strategy, a common problem in shoulder surgery is matching the humeral resection angle to the predetermined angle designed into the prosthesis. This angle may described the angle between a prosthetic collar and the diaphyseal section of the stem. In the case of a collarless stem, the angle may describe the difference between the long axis of the stem and the inferior surface of the prosthetic head. It is considered optimal for fixation and biomechanics if the resected angle and the angle of the prosthesis are identicalxe2x80x94thereby allowing intimate contact between the superior surface of resected bone and the inferior surface of the implant.
Moreover, the angular version in which the prosthesis is implanted will have a significant impact on the biomechanics of the prosthetic joint. Currently, most shoulder prosthesis systems on the market dictate the varus/valgus angle of the bone cut. This strategy does not allow the surgeon to easily alter biomechanics after the prosthesis has been trialed, much less implanted.
There are two known products currently marketed that attempt to resolve at least one of the above-noted issues. First, the Tornier-Aequalis system provides a modular junction within the metaphyseal region of the stem which allows a small block between the stem and humeral head to be interchanged. This block is available in multiple angles, thus allowing the surgeon to select the block that best fits the boney anatomy as resected. This system, however, has two primary weaknesses. First, the use of modular blocks obviously forces the design to only allow angular adjustments in finite increments. Second, the need to adjust the angle through modular blocks forces the surgeon to remove the stem, change out a component, and reset the stem. This presents inconvenience, as well as risk for interfering with resected bone and compromising fixation.
A second product currently marketed as a solution to the problems addressed above is the CenterPulse Anatomica. This product provides a humeral head that is infinitely adjustable in varus/valgus and anterior/posterior angles relative to the stem portion of the prosthesis. This is accomplished through a spherical shaped protrusion on the superior surface of the stem that fits into a spherical recess in the humeral head. These mating surfaces allows the head to be articulated about the stem, thus allowing adjustable positioning of the head. The head can be locked in a position relative to the stem. This solution provides adjustment of the neck-shaft angle as well as being able to affect adjustment of the version through flexibility in the anterior/posterior angle. The locking means, however, is sub-optimal. Particularly, the locking mechanism, requires the turning of a locking screw that has its head facing lateral and inferior, for which there is no access once the stem has been cemented. This eliminates the ability to adjust head position on the fly, and forces a total revision if articular surfaces ever need to be revised. Lastly, the protrusion on the humeral stem even when the humeral head is not in place limits the surgeon""s access to the glenoid in preparation for a glenoid replacement.
It should be appreciated that it is desired to have a prosthesis that is intraoperatively adjustable so that it can match the boney preparation. One such prosthesis that has attempted to provide this design feature is made by Sulzer Anatomica. A problem with the Sulzer Anatomica device, however, is replication of the head angular position between the trial prosthesis and the final implant is difficult. In order to alleviate this problem, Sulzer Anatomica provides a jig. The Sulzer Anatomic jig, however, is complicated and cumbersome to use.
Particularly, the Sulzer Anatomica jig has two problems. One problem is that the head position is taken directly from the long axis of the humeral stem. Thus, the trail and implant stems are required to adjust and replicate this position. This means that the Sulzer Anatomica has a large number of components to handle, and the position cannot be adjusted with the stem in vivo. Another problem is that the jig is a quite complicated table-top device. This requires transferring the implant to the back table and setting the implant (stem and head) into the jig. This is technically challenging and time consuming.
With a shoulder prosthesis that allows a surgeon to adjust the angular position of the humeral head (i.e. adjust the articular surface of the humeral head relative to the humeral stem/component and/or bone, a method must be available for trialing the prosthesis. When the trial prosthesis is implanted, several adjustments can be made to set the angular position of the prosthetic head relative to the humeral stem. A means must be available for transferring the settings obtained during the trialing process to the final implant.
What is thus needed in view of the above is a better method for trialing a shoulder prosthesis.
What is further needed in view of the above, is a trialing jig that allows the transfer of settings obtained during the trialing process to the final implant.
What is yet further needed in view of the above, is a quick and easy trialing jig that allows the transfer of setting obtained during the trialing process to the final implant.
A jig and method of use for trialing a head and conjoining portion of a humeral (shoulder) prosthesis and transferring the spatial positioning to a final implant allows a surgeon to adjust humeral head position thereof in three-dimensional space with respect to a humeral component of the humeral prosthesis that has been either previously implanted into a humerus of a patient or not. The jig utilizes a rotatable body such as a sphere that is non-translatable relative to a jig body. A trial implant construct, having a head and neck that is fixed relative to one another (is spatially positioned), is placed in the jig with the neck thereof in contact with the rotatable sphere. As the head is caused to align with markings on the jig and situated flush with the jig, the rotatable sphere replicates the angular position of the neck with respect to a fixed position head. A final implant construct whose components are not fixed relative to one another, is placed in the jig which automatically transfers the spatial positioning of the trial implant construct to the final implant construct.
According to one embodiment, the jig includes a flat plate in which is positioned a rotatable sphere. The sphere fits into the plate such that the sphere can be rotated about at least two axes that are perpendicular and extend through the center of the sphere, but which cannot translate relative to the plate. A locking means is provided to releasably lock or fix the angular position of the sphere relative to the plate by means of a set screw. The sphere has a hole extending therethrough that receives a neck or extension of a humeral head of the implant construct. The extension from the head is presented into the hole of the sphere. The sphere rotates such that the flat side of the head can rest flat upon the flat plate. The sphere is releasably locked in place and the trial implant construct is removed. A final implant construct is placed in the locked sphere. The head is rotated such that the flat side thereof rests upon the flat plate. Thereafter, the head and neck are locked in position. In this manner, the final implant construct is oriented in the same spatial position as the trial implant construct.
In one form, the subject invention provides a jig for transferring spatial positioning of a humeral head of a first construct relative to a conjoining member of the first construct to a second construct having a humeral head and conjoining member. The jig includes a body defining a flat surface, a cavity within the body, a pivoting member disposed within the cavity, the pivoting member having a configured bore accessible through the body and adapted to freely pivot within the cavity, and locking means situated in the body and adapted to selectively engage the pivoting member to releasably fix a rotational position of the pivoting member. The configured bore is adapted to receive a conjoining member of the first construct and orient the conjoining member relative to a position of the head on the flat surface of the body via pivoting of the pivoting member, the locking means releasably fixing rotational position of the pivoting member during which the first construct is removed and a conjoining member of a second construct is placed therein for alignment according to the fixed rotational position of the pivoting member as a head of the second construct is placed on the position of the head of the first construct on the body, the conjoining member then affixed to the head of the second construct.
In another form, the subject invention provides a jig for transferring spatial orientation of a humeral head to a conjoining member of a first construct to a humeral head and conjoining member of a second construct. The jig includes a body having an upper surface, a spherical cavity, and an opening in the upper surface. A sphere is disposed in the spherical cavity and has a bore configured to receive a neck of a first construct, the sphere being adapted to freely rotate within the spherical cavity and without translation relative to the body. Locking means is situated in the body and is adapted to selectively engage the sphere to releasably fix a rotational position of the sphere. The configured bore is adapted to receive a neck of the first construct and orient the neck relative to a position of the head on the flat surface of the body via rotation of the sphere, the locking means releasably fixing rotational position of the sphere during which the first construct is removed and a neck of a second construct is placed therein for alignment according to the fixed rotational position of the sphere as a head of the second construct is placed on the position of the head of the first construct on the body, the neck then affixed to the head of the second implant construct.
In yet another form, the subject invention provides a method of transferring spatial orientation of a first construct having a humeral head adapted to be releasably affixed to a conjoining member to a second construct having a humeral head adapted to be releasably affixed to a conjoining member. The method includes the steps of: (a) fixing a spatial orientation of a humeral head relative to a conjoining member of a first construct; (b) placing the conjoining member of the first construct into a jig, the jig comprising: a body defining a flat surface; a cavity within the body; a pivoting member disposed within the cavity, the pivoting member having a configured bore and adapted to freely rotate within said cavity; and locking means situated in the body and adapted to selectively engage the pivoting member to releasably fix a rotational position of the pivoting member; wherein the configured bore is adapted to receive a conjoining member of the first construct and orient the conjoining member relative to a position of the head on the flat surface of the body via rotation of the pivoting member; (c) fixing the rotational position of the pivoting member the locking means; (d) removing the first construct; and (e) placing a conjoining member of a second construct in the jig for alignment according to the fixed rotational position of the pivoting member as a head of the second construct is placed on the position of the head of the first construct on the body, the conjoining member then affixed to the head of the second construct.
The subject invention is advantageous over existing technology in that (1) the subject invention is cost effective, i.e. the subject device and/or method of use is simple in design and construction, thus reducing costs of manufacture, (2) the subject device and/or method of use is easy to use, i.e. the subject device and/or method of use essentially completes the task of trialing in three steps with no requirements for measuring angles or remembering measurements, (3) the subject invention is very compact and thus can perform trialing in an area proximate the surgical incision as opposed to transferring from/to a back table, and (4) the subject device and/or method of use is reliable, i.e. there are few moving parts to fail or loose. All of the above provides a simple, reliable, and easy to manufacture trialing system, i.e. device and/or method of use thereof.